Microwave digital phase-shifter



April 6, 1965 c. B. WATTS, JR

MICROWAVE DIGITAL PHASE-SHIFTER Filed Nov. 19, 1962 nn x LIL. 3.... Ilma 1.-; Elm., ILE... .tmwt yg w y n u y u 1 u mms. s E s um k QM A\ uw 1 m M QN Sv Nv 1 WN i, s

.l-NVENTOR. :waff-ez United States Patent O 3,177,452 MICRWAVE DIGETAL PHASE-SMFTER Chester B. Watts, Jr., Alexandria, Va., assigner to Scan- Well Laboratories, lne., Springeld, Va., a corporation of Virginia Filed Nov. 19, 1962, Ser. No. 238,612

6 Claims. (Cl. S33-31) l This invention relates to the transmission of radio frequency or microwave energy in waveguides, and more specically to the rapid control of the phase of the field associated with such energy.

It is sometimes desirable, in microwave systems, to be able to change the RF phase of the energy in a waveguide, in response to a control signal, without causing appreciable amplitude change at the same time. Such an eifect is useful, for example, in controlling the pointing angle or the beam of a phase-steerable antenna array. In the past this has been accomplished in one of several ditierent ways by devices known as variable phase-Shifters. lt is usually possible to classify such devices either as electromechanical or as non-mechanical in nature. The electromechanical types generally have relatively good RF performance but usually respond rather slowly to a control signal.

lt is an object of this invention to provide an electromechanical type of variable phase-shifter wherein the required mechanical motions are small, and the masses of the moving parts are also small, thereby permitting relatively rapid response to an electrical control signal.

A further object is to provide a variable phase-shifter responsive to a digital type of electrical control signal.

Another object is to provide a phase-shifter of rugged et relatively simple construction and which is highly efiicient and reliable in operation.

By way of example, one embodiment of this invention provides a length of rectangular waveguide wherein one wall carries a series of inward projections. The opposite wall of the waveguide is a relatively thin sheet of soft iron which is permitted limited transverse deflection. Deflection is produced by magnetic attraction of the iron wall by electromagnets positioned outside the waveguide.

ln the drawings:

HG. 1 is a central longitudinal sectional view of a complete device embodying the present invention.

FG. 2 is a cross-sectional view of the same device, taken along the line 2--2 of FIG. 1.

FIG. 3 is a graph showing typical attenuation and phase characteristics.

The exemplary device illustrated inthe drawings comprises an elongated hollow waveguide formed in part by a channel member (see FlG. 2) having a bottom wall d and side walls 2 and 6 and an upper iiexible wall formed of longitudinal llexible sections of paramagnetic material 8 and 1t?. The channel member is provided with end ilanges 7 having openings therethrough and by means of which the apparatus may be secured to other circuit components. The upper liexible wall comprising sections S and 10 is split longitudinally leaving a central groove 12 so that each section may be readily and easily tlexed. Sections S and 10 are, respectively, made up of longitudinally spaced portions 8a, Sb and Se, and 10a, 10b and 10c, the portions 8b and 10b being, for example, twice as long as 8a and 16a, and 8c and 1de being twice as long as 8b and ltlb. The portions 16a, 10b and 10c are not separately shown in the drawings but are identical to and opposite 8a, Sb and 8c, respectively. The iiexible upper wall portions are mounted to the upper edges of the side walls 2 and 6 of the channel member by being clamped thereto between those upper edges and clamping elements 1t; and 26, respectively. The elements 1S and Ztl fur ther constitute pole pieces for electromagnetic coils 1d 3,177,452 Patented Apr. 6, 1965 ice and 16. The members 18 and 20 are longitudinally spaced in accordance with the spacing of the coils 14 and 16 and are held in clamping relation to the sections S and lll by longitudinally extending bars 17 and screws 19.

The portions 8a, 3b and 8c and 10a, 10b and 10c are divided by transverse slots 44 which are bridged by conductive bridge pieces d so that all portions are electrically connected.

A central member 22 is secured in any suitable manner to the bottom wall 4 of the channel and is provided with transverse loading holes 2d from which slots extend to the upper surface of the member 22 to define a series of longitudinally spaced projections. Insulating bumper stops 2d are mounted on the projections of member 22 t0 insure a predetermined spacing between the ends of these projections and the flexible wall portions 8a, 8b, etc. when coils 1d and 1d are deenergized.

The core pieces 18 and 2li are provided with lateral ears 21 through which adjustable stops 23 are threaded. The stops 23 may be adjusted to limit upward ilexure of the wall portions 8 and 1i) when the coils 14 and 16 are energized. Y

As shown, the coils 14 and 16 and their corresponding pole pieces 18 and Ztl are uniformly spaced longitudinally of the device. As shown, the portions 8a and 1tia may be ilexed by a single pair of coils, the sections 8b and 10b are ilexed by two pairs, whereas the sections Se and 1de are exed by four pairs of coils. Thus, the magnetic force applied to each portion is proportional to its length. lt is contemplated that opposing pairs of coils 14 and 16 will be simultaneously energized, although such manner of operation is not critical nor a Alimiting feature of the invention.

A waveguide containing a periodic loading ridge of the type which has been described with reference to member 22 exhibits a band-pass characteristic illustrated typically by the solid curves in FIG. 3, wherein:

a=attenuation component of transmission =phase component of transmission fzapplied frequency fl--lower cut-olf frequency f2=upper cut-olf frequency It is found that the lower cut-off frequency f1 may be computed to good approximation by considering the structure to be a standard ridged waveguide, ignoring the effects of the loading holes. The upper cut-olf frequency f2 may be approximated by considering the periodic structure of the ridge as a low-pass filter where the cut-off is computed conventionally from the product LC. Here, L represents the inductance per section and depends upon the diameter of the holes 24, while C represents the capacitance per section and may be computed from the spacing between the ridge and the movable wall together with the area of the ridge surface facing the movable wall between adjacent holes. Longitudinal slot 12 does not appreciably affect the field within the waveguide if the `slot is narrow and well centered.

Now, if opposed movable wall sections 8, 1d are deflected outwardly as a result of energizing coils 14, 16, the cut-off frequencies both increase to new values desig nated f1 and f2. Further, it is found experimentally that, by suitably proportioning the various dimensions of the waveguide and the periodic loading ridge, the two frequency increments may be made the same: that is; f1-f1=f2f2. Thus, the phase-curve in the pass-band simply moves parallel to itself as indicated by the dotted curve of B in FIG. 3. This is a desirable condition in that it yields a sizeable region within the pass-band wherein the phase-shift introduced by the wall deilection does not change appreciably with the operating frequency.

The phase-shift produced by the device is essentially the sum of the phase-shifts of the individual sections of the movable wall. In general it is desired that the total control range correspond to 360 electrical degrees of phase-shift. Referring to FIG. 1, in order to provide a digitaltype of control, the magnet coils are operated in unison in groups containing different numbers of coils according to the various binary digits. Thusleads 30, 32 control the largest Ygroup containing, in this case, 4 pairs of coils 14 and 16, for flexing wall sections 8c and 10c. This group is capable of introducing 180 degrees of phase-shift, Yor just half the total range required of the device. 2 pairs of coils, for sections 8b and 10b. This group in troduces 90 degrees of phase-shift, and is shown in the energized Vposition as signified schematically by the battery 38. Leads 40, 42 control the smallest group containing one pair of coils, for sections 8a and 10a, capable of introducing 45 degrees phase-shift. Digital control of the total phase-shift throughout the desired S60-degree range is exercised in l45-degree steps according to the following table wherein the symbol represents an unenergized coil group while the symbol 1 represents'an energized coil group:

' Degrees n n n w 0 001 45 010 90 011 135 100 180 101 225 11,0 270 111 315 certain dimensions have been exaggerated in FIG. 1 andY FIG. 2. This applies to the thickness of the movable wall sections and to the amount of their deflection. If a movable wall section is assumed to deflect as a cantilever' of length approximately one inch, and if the wall thickness is `about .0017 inch `and the required deilection .Q20 inch,-itwil1 be found that the metal is not overly stressed and the response to a control signal will take place in a time of theforder of one millisecond. This is much faster than` other electro-mechanical types of phaseshifters presently existing.

If the deflection is limited to a `smaller value, the response time decreases. A further advantage of smaller Leads34, 36 control the next group containingl soY deflection isthat the impedance variation and resultant mismatch are less. Of course the phase-shift produced is also less,rbut this fact may be compensated for to any arbitrary extent desired simply by increasing the total number of sections in the device `without affecting the response time or impedance variation.

.While a single specific embodiment of the Yinvention has been shown and described herein, it is to be understood that the same is merely illustrative-andthat the invention may embody other formsfalling within the scope of the appended claims. 1 v.

l. A microwave phase-shifter comprising:` means deiining an elongated waveguide having three rigid and iixed conductive side walls and a flexible conductive fourth wall; the rigid wall opposite'said fourth'wall'having a longitudinal series of inwardly directed spaced conductivity projections thereon conductively connected tosaid rigid Wall; said fourth wall comprising separate sections of ferromagnetic material mounted for iiexure toward and from said projections; and separate selectively operable magnetic means adjacent said fourth wall sections, respectively, for selectively flexing said wall sections whereby to incrementally and digitally vary the distance betweenk said exible Wall sections and said projections to thereby vary the capacitance of said waveguide.

2. A device as defined in kclaim l wherein said fourth wall sections are of unequal lengths and are aligned and spaced longitudinally of said waveguide.

3. A deviceas defined in claim 2 including exible con-` ducting straps joining adjacent edge portions Of adjacent sections. i

4. A device as defined in claim 2 wherein each succeding fourth wall section is twice as long as the next preceding one whereby successive iiexure thereof effects multiple digital changes in the capacitanceof said waveguide.

5. A device as defined in claim 1 wherein each of said fourth wall sections is split longitudinally substantiallyY along its center line; said magnetic means comprising simultaneously actuable magnetic devices adjacent each half of each of said sections.

6. A device asV deiined in claim 1 including insulated stop means on said inwardly directed projections, engageable withgsaid fourth wall sections for limiting inward iiexure thereof; and adjustable stop Vmeans adjacent the outer faces of said fourth wall sections for regulating and limiting outward flexure of said sections.

References Cited by the Examiner UNITED STATES PATENTS 2,825,841 3/58 Convert 333-31 2,919,419 12/59 Rivers 333-7-83 3,118,118 1/64 waas 333 31 HERMAN KARL SAALBACH,` Primary Examiner. 

1. A MICROWAVE PHASE-SHIFTER COMPRISING: MEANS DEFINING AN ELONGATED WAVEGUIDE HAVING THREE RIGID AND FIXED CONDUCTIVE SIDE WALLS AND A FLEXIBLE CONDUCTIVE FOURTH WALL; THE RIGID WALL OPPOSITE SAID FOURTH WALL HAVING A LONGITUDINAL SERIES OF INWARDLY DIRECTED SPACED CONDUCTIVITY PROJECTIONS THEREON CONDUCTIVELY CONNECTED TO SAID RIGID WALL; SAID FOURTH WALL COMPRISING SEPARATE SECTIONS OF FERROMAGNETIC MATERIAL MOUNTED FOR FLEXURE TOWARD AND FROM SAID PROJECTIONS; AND SEPARATE SELECTIVELY OPERABLE MAGNETIC MEANS ADJACENT SAID FOURTH WALL SECTIONS, RESPECTIVELY, FOR SELECTIVELY FLEXING SAID WALL SECTIONS WHEREBY TO INCREMENTALLY AND DIGITALLY VARY THE DISTANCE BETWEEN SAID FLEXIBLE WALL SECTION AND SAID PROJECTIONS TO THEREBY VARY THE CAPACITANCE OF SAID WAVEGUIDE. 